In the fabrication of integrated circuitry, numerous devices are packed into a single small area of a semiconductor substrate to create an integrated circuit. Many of the individual devices are electrically isolated from one another. Accordingly, electrical isolation is an integral part of semiconductor device design for preventing unwanted electrical coupling between adjacent components and devices.
As the size of integrated circuits is reduced, the devices that make up the circuits are positioned closer together. Conventional methods of isolating circuit components include trench isolation. Such is typically formed by etching trenches into a semiconductor substrate and filling the trenches with insulative material. As the density of components on the semiconductor substrate has increased, the widths of the trenches have decreased. Further, it is not uncommon to find different areas of a substrate having different width and/or different depth isolation trenches. Also and regardless, some areas of integrated circuitry have greater minimum active area spacing between isolation trenches than do other areas.
Trenches are typically fabricated utilizing a trench isolation mask comprising silicon nitride and silicon dioxide. Etching of the isolation trenches essentially forms an upper corner where the trench sidewall meets the upper or outer surface of the semiconductive material within which the trenches are formed. Such can lead to several adverse effects. For example, mechanical stress is induced from the etch and can generate crystalline dislocations and dopant redistribution in such corner regions. Such can lead to a parasitic leakage path, and the sidewalls of the isolation trenches are typically roughened by the etching. Further, a typical gate oxide layer tends to thin at the sharp corners, and gate polysilicon wrap-around can generate a parasitic device with increasing corner conduction and degraded dielectric integrity.
While the invention was motivated in addressing the above identified issues, it is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretative or other limiting reference to the specification, and in accordance with the doctrine of equivalents.